在 Android 中下载背景图像需要帮助吗? [英] Need Help in Downloading in Background Images in Android?
本文介绍了在 Android 中下载背景图像需要帮助吗?的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我有一个图像视图，我写了刷卡，当时刷卡的时候，图像是从互联网下载的，所以我想我必须在刷卡之前在后台下载图像，因为我需要使用asynctask或 Service 或 IntentService，所有这些都将有助于下载和存储在 data/data/mypackages 中，但在我的情况下仍然滑动变慢任何想法，也告诉我哪个是最好的，我是否以正确的方式调用
I have an image view , i had written swiping , at that time of swiping,the images are downloading from Internet, so i thought i have to download the images in the background before swiping , for that which i need to use asynctask or Service or IntentService, all these will help in downloading and storing in data/data/mypackages , but still swiping gets slow in my case any idea, also convey me which one is best one, is it i'm calling in a right way
1.异步任务
2.服务
3.Intent Service如下图，
我很困惑哪种方法是正确的，因为我的问题仍未解决
i m confused which one is right method because still my problem not solved
这是 asynctask 代码示例片段
public class Demo extends Activity {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
new FirstTask().execute(); // calling Asynctask here
}
}
异步任务代码
private class FirstTask extends AsyncTask<Void, Void, Void> {
private final ProgressDialog dialog = new ProgressDialog(Catalogue.this);
int temp = 0;
// can use UI thread here
protected void onPreExecute() {
this.dialog.setMessage("Loading...");
this.dialog.setCancelable(false);
//this.dialog.show();
System.gc();
Toast.makeText(Catalogue.this, "My Async Created",
Toast.LENGTH_LONG).show();
}
@Override
protected Void doInBackground(Void... params) {
Looper.prepare();
try {
myddownloadmethod();// calling my download method
} catch (Exception e) {
Util.trace("Error in Async"+e.getMessage());
}
Looper.loop();
return null;
}
protected void onPostExecute(Void result) {
if (this.dialog.isShowing()) {
Toast.makeText(Catalogue.this, "My Async destroyed",
Toast.LENGTH_LONG).show();
Toast.makeText(Catalogue.this, "count" + temp,
Toast.LENGTH_LONG).show();
this.dialog.dismiss();
}
}
}
这是我的服务摘要
public class MyService extends Service implements Runnable
{ @Override
public void onCreate() {
super.onCreate();
Thread mythread = new Thread(this);
mythread.start();
}
public void run() {
Looper.prepare();
try {
myddownloadmethod();// calling my download method
} catch (Exception e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
Looper.loop();
}
@Override
public IBinder onBind(Intent intent) {
// TODO Auto-generated method stub
return null;
}
}
Invoking Service
public class ServicesDemo extends Activity {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
startService(new Intent(this, MyService.class));
}
}
这是 IntentService 代码
public class Downloader extends IntentService {
public Downloader() {
super("Downloader");
}
@Override
public void onCreate() {
super.onCreate();
}
@Override
public void onDestroy() {
super.onDestroy();
}
@Override
public void onHandleIntent(Intent i) {
try {
myddownloadmethod();// calling my download method
} catch (Exception e1) {
// TODO Auto-generated catch block
Log.d("Error",e1.getMessage());
}
}
}
从 MyActivity 调用 IntentService
Calling IntentService from MyActivity
public class ServicesDemo extends Activity {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Intent i1=new Intent(this, Downloader.class);
startService(i1);
}
}
推荐答案
使用服务下载它的最佳方式，就像我从服务器下载文件并放入 SD 卡所做的那样，也使用它的通知.这是一段很长的代码，但我认为是完美的代码，如果有什么不明白的地方，请访问 android 开发者博客获取服务.
The best way to download it using the service like i have done to download the file from server and put in SD card also use the notification for it. It is quite long code but i think the perfect one,if did not understand any thing then please go to android developer blog for services.
public class DownloadService extends Service{
SharedPreferences preferences;
private static final String DOCUMENT_VIEW_STATE_PREFERENCES = "DjvuDocumentViewState";
private Looper mServiceLooper;
private ServiceHandler mServiceHandler;
private NotificationManager mNM;
String downloadUrl;
public static boolean serviceState=false;
// Handler that receives messages from the thread
private final class ServiceHandler extends Handler {
public ServiceHandler(Looper looper) {
super(looper);
}
@Override
public void handleMessage(Message msg) {
downloadFile();
showNotification(getResources().getString(R.string.notification_catalog_downloaded),"VVS");
stopSelf(msg.arg1);
}
}
@Override
public void onCreate() {
serviceState=true;
mNM = (NotificationManager)getSystemService(NOTIFICATION_SERVICE);
HandlerThread thread = new HandlerThread("ServiceStartArguments",1);
thread.start();
// Get the HandlerThread's Looper and use it for our Handler
mServiceLooper = thread.getLooper();
mServiceHandler = new ServiceHandler(mServiceLooper);
}
@Override
public int onStartCommand(Intent intent, int flags, int startId) {
Log.d("SERVICE-ONCOMMAND","onStartCommand");
Bundle extra = intent.getExtras();
if(extra != null){
String downloadUrl = extra.getString("downloadUrl");
Log.d("URL",downloadUrl);
this.downloadUrl=downloadUrl;
}
Message msg = mServiceHandler.obtainMessage();
msg.arg1 = startId;
mServiceHandler.sendMessage(msg);
// If we get killed, after returning from here, restart
return START_STICKY;
}
@Override
public void onDestroy() {
Log.d("SERVICE-DESTROY","DESTORY");
serviceState=false;
//Toast.makeText(this, "service done", Toast.LENGTH_SHORT).show();
}
@Override
public IBinder onBind(Intent intent) {
// We don't provide binding, so return null
return null;
}
public void downloadFile(){
downloadFile(this.downloadUrl,fileName);
}
void showNotification(String message,String title) {
// In this sample, we'll use the same text for the ticker and the expanded notification
CharSequence text = message;
// Set the icon, scrolling text and timestamp
Notification notification = new Notification(R.drawable.icon, "vvs",
System.currentTimeMillis());
notification.flags |= Notification.FLAG_AUTO_CANCEL;
Intent intent = new Intent(this, HomeScreenActivity.class);
intent.setFlags (Intent.FLAG_ACTIVITY_CLEAR_TOP);
//The PendingIntent to launch our activity if the user selects this notification
PendingIntent contentIntent = PendingIntent.getActivity(this.getBaseContext(), 0,
intent, PendingIntent.FLAG_CANCEL_CURRENT);
// Set the info for the views that show in the notification panel.
notification.setLatestEventInfo(this, title,
text, contentIntent);
// Send the notification.
// We use a layout id because it is a unique number. We use it later to cancel.
mNM.notify(R.string.app_name, notification);
}
public void downloadFile(String fileURL, String fileName) {
StatFs stat_fs = new StatFs(Environment.getExternalStorageDirectory().getPath());
double avail_sd_space = (double)stat_fs.getAvailableBlocks() *(double)stat_fs.getBlockSize();
//double GB_Available = (avail_sd_space / 1073741824);
double MB_Available = (avail_sd_space / 10485783);
//System.out.println("Available MB : " + MB_Available);
Log.d("MB",""+MB_Available);
try {
File root =new File(Environment.getExternalStorageDirectory()+"/vvveksperten");
if(root.exists() && root.isDirectory()) {
}else{
root.mkdir();
}
Log.d("CURRENT PATH",root.getPath());
URL u = new URL(fileURL);
HttpURLConnection c = (HttpURLConnection) u.openConnection();
c.setRequestMethod("GET");
c.setDoOutput(true);
c.connect();
int fileSize = c.getContentLength()/1048576;
Log.d("FILESIZE",""+fileSize);
if(MB_Available <= fileSize ){
this.showNotification(getResources().getString(R.string.notification_no_memory),getResources().getString(R.string.notification_error));
c.disconnect();
return;
}
FileOutputStream f = new FileOutputStream(new File(root.getPath(), fileName));
InputStream in = c.getInputStream();
byte[] buffer = new byte[1024];
int len1 = 0;
while ((len1 = in.read(buffer)) > 0) {
f.write(buffer, 0, len1);
}
f.close();
File file = new File(root.getAbsolutePath() + "/" + "some.pdf");
if(file.exists()){
file.delete();
Log.d("FILE-DELETE","YES");
}else{
Log.d("FILE-DELETE","NO");
}
File from =new File(root.getAbsolutePath() + "/" + fileName);
File to = new File(root.getAbsolutePath() + "/" + "some.pdf");
} catch (Exception e) {
Log.d("Downloader", e.getMessage());
}
这篇关于在 Android 中下载背景图像需要帮助吗?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
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